Synthesis of Biodiesel/Bio-Oil from Microalgae - Biotechnological Applications of Microalgae - page 100

transesterification for the synthesis of biodiesel. The species of microalgae employed
for the production of biofuel include Chlorella vulgaris , Chlorella sorokiniana ,
Sargassum patens C., and Spirulina . The method of biodiesel production from algal
biomass can be done either by direct transesterification or in two steps involving
the extraction of oil from algae followed by transesterification. Economic in situ
transesterification of the microalgae has been adopted that involves combining the
two steps of lipid extraction and transesterification into a single step. Direct trans-
esterification of the microalgae after cell disruption by sonication resulted in a high
conversion of biodiesel (97.25%). The fuel properties of the biodiesel synthesized
from the microalgal oil derived from Chlorella protothecoides showed high fuel
quality with a cold filter plugging point of −13°C. A high composition of unsaturated
fatty acid methyl ester content in the microalgal oil methyl esters (MOME) (i.e.,
90.7 wt%) led to a low oxidation stability of the fuel (4.5 h). The chemical treatment,
pyrolysis, or thermochemical catalytic liquefaction of microalgal oil for the synthe-
sis of bio-oil eliminates the dewatering and drying steps. The major constituents of
bio-oil obtained from brown microalgae Sargassum patens C. Agardh by hydrother-
mal liquefaction consist of carbon (64.64%), followed by oxygen (22.04%), hydrogen
(7.35%), nitrogen (2.45%), and sulfur (0.67%).
The alga belongs to the third-generation feedstock for the synthesis of a renewable
fuel, biodiesel, or bio-oil. The first generation of feedstock was the crop species, and
second-generation feedstock consisted of grasses and trees, which principally consisted
of lignocellulosic biomass. With the limited availability of crop species, the focus of
recent research has been on second- and third-generation feedstocks (Stephenson et al.,
2011). Second-generation feedstocks have certain constraints that involve breaking the
complex structure of lignin and converting the crystalline cellulose to amorphous
cellulose. The process involved in second-generation biofuels makes it quite energy
intensive. Hence, the focus of the research to a large extent in recent years has been on
third-generation feedstocks, that is, microalgae (Lam and Lee, 2012). The conversion
of microalgal lipids into biodiesel is a holistic approach that begins with the identifica-
tion of an appropriate microalgal species that has a high potential to accumulate oil
within the cells. The oil consists of crude lipids and neutral lipids. Neutral lipids con-
sist of triglycerides, free fatty acids, hydrocarbons, sterols, wax and sterol esters, and
free alcohols. Among these, only triglycerides and free fatty acids are saponifiable, and
hence can be converted to biodiesel by esterification or transesterification. Crude lipids
consist of neutral lipids along with pigments (Sharma et al., 2011). The triglycerides
and free fatty acids are the part of microalgal lipids that can be converted to biodiesel
or bio-oil. The microalgal biomass can be used for the production of biofuel, either by
pyrolysis or through direct combustion or thermochemical liquefaction in which bio-
oil is produced. Alternatively, the lipid can be derived from microalgal biomass and
converted to biodiesel via transesterification (Kao et al., 2012).
In general, microorganisms that accumulate more than 20% to 25% of their weight
as lipid are called oleaginous species (Kang et al., 2011). As these oleaginous micro-
organisms can accumulate a large amount of oil within their cells, they can be very
good feedstocks from which to extract oil and lipids that can be converted to biofuel
(bio-oil or biodiesel). In some of the algae, the lipid content may be as high as 75%
of their dry biomass. Most species of algae produce triglycerides (that can be utilized